Stdies are being carried out to determine whether dietary modification and streptozotocin induced diabetes influence the rate of microsomal fatty acyl-CoA desaturation and chain elongation. The same modifications are being employed to determine whether these conditions influence the apparent turnover rate of the component parts of rat liver ethanolamine and choline phosphoglycerides. In addition, studies have been carried out to define what regulates the microsomal chain elongation of fatty acids. A variety of different unsaturated fatty acids have been prepared by total organic synthesis and used as substrates to define the type of substrate specificity which exists for this metabolic process. Model substrates have also been employed to define how structural modification mediates the beta-hydroxyacyl-CoA and 2-trans-enoyl-CoA reductase reactions.